1. Field of the Invention
The present invention pertains to the field of circuit board connectors. More particularly, the present invention pertains to stacking circuit board connectors for high speed signaling.
2. Description of Related Art
Improving the overall signal transfer characteristics of circuit board connectors can allow higher frequency signals to be transferred through such connectors. As a result, system level signal frequencies may be raised when an improved connector is employed in a system where the connector would otherwise limit the speed of system communication.
Stackable connectors are connectors which allow circuit boards that are substantially parallel to be connected. A cross sectional view of a ground pin of one prior art stackable connector is shown in FIG. 1. The prior art connector connects ground, power, and signal lines from one circuit board 160 to another circuit board 170 via a mating plug and receptacle arrangement. When a receptacle housing 105 engages a plug housing 100, plug pins 120 and 130 contact their respective receptacle pins 140 and 150. Although there is a gap shown beneath the plug housing 100 in this cross-sectional view, the housing 100 is typically attached to the circuit board 170 at both ends, beyond the last contact.
The pin 120 has a beam portion 122 which has a solder foot 176 extending beyond the plug housing 100 for soldering to the circuit board 170 at a solder point 172. The pin 120 is thus connected to a signal line 174 in the circuit board 170. A nib 115 may be included for some signal lines (e.g., a ground signal line) to contact an optional electromagnetic interference (EMI) shield 110 which is useful for limiting radio frequency radiation from the connector.
The pin 120 has an elongated portion 124 connected substantially perpendicular to the beam portion 122. The elongated portion extends outwardly away from a vertical center of the housing 100. A contact portion 126 is pressed against the receptacle pin 140 by an S-shaped portion 128. The second signal pin 130 is similarly configured.
The receptacle portion includes the receptacle housing 105 which supports the receptacle pins 140 and 150 as well as the optional EMI shield 110. The EMI shield 110 is also typically supported by plastic protrusions spaced along its length. The receptacle pin 140 includes a solder foot 142 which allows the contact 140 to be connected to the circuit board 160 at a solder point 162, establishing an electrical connection between the contact 140 and a signal line 166 in the circuit board 160. The receptacle pin 150 is similarly configured to make an electrical connection with a signal line 168 via the solder connection 164.
A prior art signal pin is similar to the illustrated ground pin except that there is no nib which contacts the plug pin to the optional EMI shield 110. No particular arrangement of ground and signal pins is typically required in the prior art, except when the optional EMI shield 110 is used, The EMI shield 110 is designed to contact every tenth pin, forcing that pin to be a ground pin. Thus, while the prior art allows power, ground, and signals to be transmitted between the two boards, the impedance of the signal/contact interface and the overall connector structure is not carefully controlled.
The prior art stackable connector fails to provide metal shields which surround signal pins at a desired distance to tune the characteristic impedance of the signal pin. Furthermore, the prior art does not allow ground planes to be brought sufficiently close to signal pins in stackable connectors due to the typical thickness of the housing 105 and the lack of any shielding mechanism on at least the inward side of the signal pins.
An improved stacking connector is disclosed. The connector includes a plug portion and a receptacle portion. The plug portion includes a plug signal pin and a plug impedance control pin located adjacent to the plug signal pin. The receptacle portion includes a receptacle signal pin for engaging the plug signal pin when the plug portion and the receptacle portion are in a mated position. The connector also includes an impedance control shield which is located adjacent to the plug signal pin or the receptacle signal pin.